The invention relates to grooving of rubber tires used on various vehicles, including trucks and other motor vehicles. The invention more particularly relates to a cutting head member for a resistance-heated tire groover. The invention also relates to a resistance-heated tire groover that incorporates the disclosed cutting head member and facilitates grooving of rubber tires in a rapid, efficient, and precise manner.
It has long been known that tires for various vehicles, although worn smooth as a result of extended operation on abrasive road surfaces, nonetheless retain significant amounts of rubber on their circumferential surfaces so that new tread patterns may be cut or "grooved" into such surfaces, thereby allowing the tires to be returned to service and their operable lives extended for thousands of additional miles. Grooving of tires has been particularly prevalent in the trucking industry, where tractor/trailer vehicles can have up to 18 large tires, each of which costs several hundred dollars when purchased new. Obviously, a grooving technique that allows such tires to be rejuvenated so that their operable lives are significantly extended has found great favor with tractor/trailer owners and operators.
Previous tire groovers most often have operated by means of a heated cutting blade that slices through the rubber material on the circumferential surface of the tire being grooved. Within this broad approach, there exists two distinctly different types of construction for heating the cutting blade of a groove device.
In the first type of groover construction, heat is transferred to the cutting blade by means of a conduction heating element that generally is interposed within the metal structure of the groover, such that heat is conducted from the heating element, through some portion of the body of the apparatus, into a cutting head member, and thereafter into an attached cutting blade. Thus, in Van Alstine, U.S. Pat. No. 2,240,382, and Van Alstine, U.S. Pat. No. 2,618,056, there is disclosed generally a tire grooving tool having handles attached at each end of a hollow metal tube, with a conduction heating element concentrically interposed within the hollow metal tube at its approximate longitudinal center point, with the hollow metal tube passing through a metal cutting head that retains a cutting blade. In these devices, the heating element conducts heat radially through the walls of the metal tube, into the metal cutting head, and finally into the cutting blade mounted in the cutting head.
In Olson, et al., U.S. Pat. No. 2,254,975, there is disclosed a tire groover having a hollow metal barrel member within which a heating element is interposed, so that heat is conducted from the heating element longitudinally through the barrel member into a cutting head member at the end of the barrel member, and thereafter into a cutting blade attached to the cutting head. Similarly, in Mertens, U.S. Pat. No. 2,230,042, there is shown a tire groover having a heating element interposed within a barrel member with a cutting head member and cutting blade at the end of such barrel member, so that heat is conducted from the heating unit through the barrel member, into the cutting head member, and finally into the cutting blade.
Although tire groovers of the conduction-heating type described above are capable of suitable operation under certain circumstance, the performance of such tire groovers is deficient in several ways. Specifically, transferring heat into a cutting blade by conduction is inherently inefficient, since the heat generated by the heating element is conducted not only into the cutting blade, but also into the various other parts of the devices. In addition, heat constantly is lost to the surrounding environment by means of convection heat transfer occurring over substantially the entire surface area of the devices.
As a result of these inherent inefficiencies, it has developed that, as the cutting blades of conduction-heated tire groovers are passed through the rubber of a tire being grooved, heat is transferred from the cutting blade to the rubber at a rate that generally exceeds the rate at which heat is conducted into the blade by the heating element. In such instances, the cutting blade is rapidly cooled down to the point that continued grooving becomes difficult.
In the second type of groover construction, heat is directly generated in the cutting blade by means of a resistance-heating effect as electrical current from an external source is conducted through the cutting blade. Thus, in Ruff, U.S. Pat. No. 2,896,059, there is disclosed a tire groover wherein the ends of a U-shaped cutting blade are secured in separate electrical contact members of a cutting head, each of which contact members is electrically insulated from the other. In operation, electrical current is conducted from one of the contact members, through the cutting blade, and into the other contact member. As the electrical current passes through the blade, heat is generated within the blade as a result of resistance to the flow of electrical current through the blade.
Resistance-heated tire groovers provide the benefit of more heat being generated in the cutting blade as compared to the cutting blades of conduction-heated groovers. This in turn results in more rapid and efficient tire grooving than is possible with conduction-heated devices. However, the increased amount of heat generated in the cutting blades of resistance-heated groovers has been shown to have the disadvantage of causing the material of the cutting blades to deteriorate rapidly to the point that the the cutting blades often became heat-damaged or burn out, thereby rendering the particular groover inoperable until the cutting blade is replaced. The replacement of cutting blades in previously-known resistance-heated groovers is difficult and time-consuming, in that bolts or screws must be loosened with a wrench, screwdriver, or other working tool, and thereafter retightened, in order to replace a cutting blade. The frequency of this difficulty is increased by the fact that, in addition to replacing burned-out cutting blades, it often is necessary to adjust or replace cutting blades in order to effect different tread depths or patterns during a particular grooving operation.
Another disadvantage of previously-known resistance-heated groovers is that the means of energizing and de-energizing such devices, and thereby controlling the generation of heat in the cutting blades, is awkward and cumbersome and tends to slow grooving of tires. This is because the switch actuators of previously-known resistance groovers either are remotely located at the external current source or are so situated on the devices themselves that the operator must alter or interrupt a grooving operation in order to energize or de-energize the grooving device. Thus, it is extremely difficult to control and regulate precisely the generation of heat in the cutting blades of such devices, which slows grooving operations and increases the frequency at which cutting blades become heat-damaged or burn out.